Embodiments described in International Publication Number WO 2011/034614 A2 generate synthetic base station data which preserve the integer nature of carrier phase data. (See for example Part 11 and Parts 2, 7.2, 7.5, 7.8, 8.8, 9.6.4, 12.1, 12.2 and 12.6 of WO 2011/034614 A2.) A set of corrections is computed per satellite (a Melbourne-Wübbena bias, a code leveled clock error and a phase leveled clock error) from global network data. Using these corrections, a rover can use the Melbourne-Wübbena (MW) linear combination to solve widelane ambiguities and use ionospheric-free code/phase observations to solve the narrowlane ambiguities. With fixed ambiguities, the rover can achieve cm-level accuracy positioning in real-time.
An advantage of this approach is that it is insensitive to ionospheric activity, as no ionosphere information is required—all observation combinations used in the network and rover processes are ionospheric-free.
A disadvantage is that the convergence time is longer than desired, typically 10-15 minutes to attain 2-5 cm rover position accuracy, due to the lack of ionosphere information. Another disadvantage of this approach is that the generated synthetic data cannot be used for single-frequency data processing without modifying existing rover data processing software.